Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	$ 261	$ 249
Derivatives	86	208
Total Assets at Fair Value	347	457
Derivatives	172	102
Total Liabilities at Fair Value	172	102
Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	261	249
Derivatives	17	104
Total Assets at Fair Value	278	353
Derivatives	160	101
Total Liabilities at Fair Value	160	101
Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	0	0
Derivatives	69	104
Total Assets at Fair Value	69	104
Derivatives	12	1
Total Liabilities at Fair Value	12	1
Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	0	0
Derivatives	0	0
Total Assets at Fair Value	0	0
Derivatives	0	0
Total Liabilities at Fair Value	$ 0	$ 0